How do you filter air when the electricity is low or non-existent?

Jonnie PekelnyContributor - June 28, 2020

In trying  to figure out how to power my CPAP machine in an extended electrical outage, I started thinking about what other essential, electrical gadgets I might need to run. Mostly I’ve been assuming that I’ll just make do with portable battery-driven devices for things like flashlights and solar powered power banks for my cell phone and tablet. But then I thought, it would be really good to be able to run my fan in hot weather. And… I thought, I might really need to run my air filter.

Here, in Northern California, we’ve been having power outages instigated by our power company. Most of these happen in fire season to, supposedly prevent wildfires from happening, but they do anyway. Really bad fires lately. So, it’s entirely possible to have a scenario where the electricity is out, but we’re supposed to keep our windows closed and are supposed to be filtering the air which is full of unhealthy particulates.

How do you filter the air if there’s no electricity?

I recently measured how much power my air filter uses and it’s kind of a power hog. It uses nearly as much as my CPAP, but, unlike a CPAP I would have to run the air filter either all day or at least for 12 or so hours a day. I can’t really afford a battery that keeps both my CPAP and my air filter running every day.

I’m wondering whether any of you out there have any suggestion for how to approach this problem.

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I could double-check the generator thread, but if the air filter is in the same vicinity as CPAP for total kwh consumption, you would probably have sufficient capacity for both with the larger yeti and 400 watts of solar input.

Indoor air quality (IAQ) is an already super-complicated topic that gets even more complicated when you add spikes in outdoor contaminants and power loss. Individual circumstances are pretty different, so I’m going to keep comments broad, and you can add specifics related to your situation.

What are the contaminants you’re trying to manage that require the air filter? Could you potentially lean less heavily on the filter by addressing other things? A good assessment of IAQ would include:

1. Source control. Basically avoid bringing bad stuff into the house. If you’re not already familiar with it, check out the lumber liquidators formaldehyde controversy from a few years ago. In your case I would extend this to mean that you need a tight building enclosure to ensure that you minimize the quantity of outdoor contaminants entering the house. And for the love of god don’t let people wear shoes in your house!
2. Local ventilation. Exhaust fans ducted to outdoors at kitchens and bathrooms. But you have to be careful with this when there are outdoor contaminants!!! When you turn on an exhaust fan the air that’s sucked out is replaced by air from outside. With tight building enclosures some people think the enclosure can have a filtering effect roughly equivalent to a MERV 10 filter, which might be OK in your case. But you want to make certain that the exhaust fans aren’t pulling in air that’s more contaminated than the air the outgoing air.
3. A continuous supply of fresh air for the building occupants. Again this is very tricky when outdoor air quality is crappy. You can potentially filter the incoming air stream provided the particulate is big enough to be filtered by the HVAC filter. Some heat/enthalpy recovery ventilators (HRV/ERV) have filters, and central fan integrated supplies (CFIS) can be ducted to the filter on your existing heating or cooling system. IMO, the overall best system for most people is a CFIS connected to a variable speed furnace/ac fan with a MERV 14 filter. In tight enclosures this will slightly positively pressurize the house, which buffers against existing the infiltration of contaminants from the outside (including radon). But this can be expensive, so might be more of a long-term thing.

Working from my memory of the evidence, air filters improve air quality, but not as much as high quality HVAC filters. So if you have ducted HVAC, adding a MERV 14 or better filter will likely have a higher impact than running the air filter. And running a variable speed fan at very low speeds will probably consume less energy than running an air filter (would guess 10-30 watts for VS fan on low). Otoh, connecting these to small-scale back-up power isn’t highly viable for a layperson. And the relative impact of either is low when contrasted with the impact of the other three strategies above.

Depending on duration of poor outdoor air quality and advance notification you might try to ride out much of the outage with minimal filtration by turning over the air as much as possible in the house prior to the loss of outdoor air quality. Then allow for minimal air infiltration once the power is out and the outdoor air quality is poor. One of the major drivers for air infiltration is pressure problems associated with heating/cooling duct systems, so leave interior doors open to minimize infiltration driven by air equipment. Also, IAQ problems are often significantly driven by ducts located in unconditioned space (esp attics). If you have ducts in unconditioned spaces, at minimum you should meticulously seal them to ensure they can’t drive bad stuff into the home.

Might be a bit kooky, but IIRC Cresson Kearny developed a manual air pump to turn over the air in the expedient fall-out shelters he developed. He claimed some really high cubic feet/minute numbers. I’ve never built one, but they look super basic, and could be potentially connected to a filter. I believe there are contemporary manual air pumps that you can also buy pretty inexpensively. Would need to connect to a duct and filter on incoming side. Might be an interesting diy weekend project. https://en.wikipedia.org/wiki/Kearny_air_pump

 

I could double-check the generator thread, but if the air filter is in the same vicinity as CPAP for total kwh consumption, you would probably have sufficient capacity for both with the larger yeti and 400 watts of solar input.

Indoor air quality (IAQ) is an already super-complicated topic that gets even more complicated when you add spikes in outdoor contaminants and power loss. Individual circumstances are pretty different, so I’m going to keep comments broad, and you can add specifics related to your situation.

What are the contaminants you’re trying to manage that require the air filter? Could you potentially lean less heavily on the filter by addressing other things? A good assessment of IAQ would include:

1. Source control. Basically avoid bringing bad stuff into the house. If you’re not already familiar with it, check out the lumber liquidators formaldehyde controversy from a few years ago. In your case I would extend this to mean that you need a tight building enclosure to ensure that you minimize the quantity of outdoor contaminants entering the house. And for the love of god don’t let people wear shoes in your house!
2. Local ventilation. Exhaust fans ducted to outdoors at kitchens and bathrooms. But you have to be careful with this when there are outdoor contaminants!!! When you turn on an exhaust fan the air that’s sucked out is replaced by air from outside. With tight building enclosures some people think the enclosure can have a filtering effect roughly equivalent to a MERV 10 filter, which might be OK in your case. But you want to make certain that the exhaust fans aren’t pulling in air that’s more contaminated than the air the outgoing air.
3. A continuous supply of fresh air for the building occupants. Again this is very tricky when outdoor air quality is crappy. You can potentially filter the incoming air stream provided the particulate is big enough to be filtered by the HVAC filter. Some heat/enthalpy recovery ventilators (HRV/ERV) have filters, and central fan integrated supplies (CFIS) can be ducted to the filter on your existing heating or cooling system. IMO, the overall best system for most people is a CFIS connected to a variable speed furnace/ac fan with a MERV 14 filter. In tight enclosures this will slightly positively pressurize the house, which buffers against existing the infiltration of contaminants from the outside (including radon). But this can be expensive, so might be more of a long-term thing.

Working from my memory of the evidence, air filters improve air quality, but not as much as high quality HVAC filters. So if you have ducted HVAC, adding a MERV 14 or better filter will likely have a higher impact than running the air filter. And running a variable speed fan at very low speeds will probably consume less energy than running an air filter (would guess 10-30 watts for VS fan on low). Otoh, connecting these to small-scale back-up power isn’t highly viable for a layperson. And the relative impact of either is low when contrasted with the impact of the other three strategies above.

Depending on duration of poor outdoor air quality and advance notification you might try to ride out much of the outage with minimal filtration by turning over the air as much as possible in the house prior to the loss of outdoor air quality. Then allow for minimal air infiltration once the power is out and the outdoor air quality is poor. One of the major drivers for air infiltration is pressure problems associated with heating/cooling duct systems, so leave interior doors open to minimize infiltration driven by air equipment. Also, IAQ problems are often significantly driven by ducts located in unconditioned space (esp attics). If you have ducts in unconditioned spaces, at minimum you should meticulously seal them to ensure they can’t drive bad stuff into the home.

Might be a bit kooky, but IIRC Cresson Kearny developed a manual air pump to turn over the air in the expedient fall-out shelters he developed. He claimed some really high cubic feet/minute numbers. I’ve never built one, but they look super basic, and could be potentially connected to a filter. I believe there are contemporary manual air pumps that you can also buy pretty inexpensively. Would need to connect to a duct and filter on incoming side. Might be an interesting diy weekend project. https://en.wikipedia.org/wiki/Kearny_air_pump

 

Let me try to make this a little simpler (for me anyway). My overriding reason for having an air filter is that I live in Northern California, about an hour or two away from where some of the worst wildfires have happened in the past few years. In two consecutive years, the air quality in my whole region during these fires was TERRIBLE. At one point the worst on the planet. I am actually not in the areas usually hit worst, but it’s bad enough! In 2017 there were many days when we weren’t even supposed to go outside, and you hardly wanted to because of all the smoke in the air.

Additional complications: I live in a 100 year old house with lots of air leaks and I am a person who can’t bear to live for long stretches of time with windows closed. I particularly can’t sleep with a closed window. I have to open it at least a little.

I got the air filter after the last round of fires thinking I really need to be prepared to hunker down in a room and keep the air as fresh as possible there. I haven’t used it for real yet (only to measure electrical load) so I don’t know how long I would need to run it or at what speed. I did a test of the electrical usage for the filter at its highest speed. It was 53 watts over the course of an hour (compared to 41 watts for my CPAP). I haven’t tried testing it at its lower settings.

CPAP use and air filtration if the air is bad enough are neck in neck for me as first priorities in an extended power outage. If the air is bad enough I would take the air filtration over CPAP, although so far I’ve managed without it, so I guess it has to get pretty bad.

The solar generator I’m eyeing at the moment is the Ecoflow Delta which has a total Wh rating of around 1300, so about 1000 of that is usable. It does charge very fast if you have it rigged up to enough solar panels — which I probably won’t have all of at the beginning because I can’t afford it. I could run both the CPAP and the air filter for some time on that power, and hope I can recharge it quickly in a day or so before I run out of watt hours. The problem with air filters is that you’re really supposed to run them for a big chunk of the time. Some people advise 12 hours, some 24/7!

So, okay. If I get out of the technicalities, the basic question for me is, what do I do if there are wildfires, the air has gotten really bad, and the power goes out? This is actually a very realistic scenario since our power company has been shutting off the power at exactly such times. They tell people to stay inside and use their air filters and then they shut off the electricity! My specific house has never been affected by that, but it could be. In the past I’ve managed without air filtration partly by leaving the area (harder to do during COVID-19) and partly by just wearing a mask in the house part of the time and hoping for the best. That’s low tech, but doesn’t feel quite secure.

 

This is a tough one. To clarify, the air filter uses 53 watts of power (on high) continuously when it’s running, right? So if you ran it 24 hours/day, we would expect it to use about 1.3 kwh/day, right? If you could throttle this back to 12 hours/day you’d likely be fine with solar generator and 400 watts of solar also running cpap. Remember from the generator thread that on an average summer day 400 watts of solar will produce ~2 kwh. My cursory search suggests that being in not very close proximity to forest fires will diminish solar output by ~12%, which isn’t a huge hit. https://s.campbellsci.com/documents/us/miscellaneous/forest-fire-impact-on-solar-pv.pdf

Other questions:

1. How do you heat and cool your home?
2. Any ducts in either an attic or foundation crawlspace?
3. Do you leave windows open during the forest fire?
4. House was built in 1920s? Stick-framed? What’s exterior finish? Ever had air leakage tested with a blower door?
5. How long do the fires generally last?

This is probably nothing ground-breaking, but worth a read: https://newscenter.lbl.gov/2019/10/25/improving-indoor-air-quality-during-wildfires/ Does’t solve the problem of power outage though.

 

Jesse, I’ve delayed in answering your questions because I’m actually not very clear on my own situation. And, in the interest of full disclosure, I’m also trying to help an important person in my life (sort of a teacher) to deal with these power outages. She lives closer to the fires and is in older than I am and in somewhat more fragile health. So, I’m trying to answer the questions for both of us.

She is in greater danger of power outages (they had two last year) and more in harm’s way of the smoke. Last year the power outages happened on hot smoky days and the longer of them lasted for four days. When the power isn’t out she runs her air filters 24/7 during the fires, initially on high for a week and then on a lower setting. I’m not sure if she also runs them when fire season isn’t on. She uses multiple filters but I guess she would need at least one. That’s hard to accommodate even with a generator, which I’m not sure she can have because she lives in a townhouse.

For me, I haven’t yet had to use my air filter. I got one a couple of years ago when it became apparent that these catastrophic fires were becoming the new normal. But I live a bit farther from the fires. The air can still get very bad, but my power hasn’t been turned off so far (though a friend 3/4 mile away from me did lose her power). To date I’ve managed without using my air filter. One year I made do with a mask and keeping the windows mostly closed, though I did open them sometimes anyway and also my house really leaks air. Another year, when the air was particularly bad I went 20 miles farther away from the fires and stayed with my mom. That would be hard to do now because of COVID-19.

So, I’m not sure exactly what I would do if the air got bad, the power went out and I couldn’t go somewhere else. If my teacher’s experience with air filters is to be trusted then they do need to stay on 24/7 to be effective. So, I guess I’d designate a “clean air” room and try to run them all the time. But the solar “generator” I just got would get maxed out pretty quickly from 24/7 use on high. It only has about 900+ usable watt hours.

Answers to your questions:

1) Heating is via an old forced air gas heater for most of the house. The heater is in the basement. There is also an upstairs room that has its own gas heater. Cooling is just fans for me, but my housemate (upstairs room) has a window air conditioner unit.

2) No

3) Sometimes. It’s inadvisable, but I really don’t like an unventilated house, even knowing as I do that air is coming in through all kinds of cracks. So, I sometimes “cheat” — particularly when I sleep.

4) I assume stick-framed, but I actually don’t know (?). Exterior is wood siding. I don’t know what a blower door is. There is no question that the house leaks air. Like, at least one window doesn’t quite close all the way.

5) This is a hard question to answer. In the last few years, fire season has meant multiple catastrophic fires in different parts of the state. Some  of them get put out farily quickly while others burn for weeks. Then the air situations is an accumulation of these fires plus whatever weather conditions encourage or discourage it. In 2017 the air was terrible for about two weeks.

Then there’s the questions of PG&E (power company) induced proactive power outages. They started that last year. Last year was a mess. They shut off power with little warning and little information to different parts of the state on at least two or three occasions causing a lot of chaos and stress. They’ve told us that this will keep happening for the next 10 years. Really?

 

Yeah, super hard. Some thoughts.

1. Get the air turned over a lot before the outdoor air quality turns bad. 

2. When air quality turns bad, filter while you still have power. If your old furnace has a well-sealed filter rack I would probably install a MERV 14 filter, then turn the fan on the tstat to “on” during periods when you have power and declining outdoor air quality. Remember, this is likely more effective than the air cleaners. However, other readers should note that this could potentially be a poor strategy in homes where a considerable fraction of the duct system is located outside the conditioned space (attics, vented crawlspaces). Also note, MERV 14 filters are more restrictive than standard filters so you may find that you can’t run a higher MERV filter to actually heat your house in the winter. Most furnaces will tell you this by cycling on “high limit” in winter, which causes the furnace to shut down prematurely due to high temperatures at the heat exchanger (low airflow). So be prepared to switch back to your previous filter in winter.

One other constraint with running furnace fan is that it can drive pressurization & depressurization of rooms when interior doors are closed. This is why so many houses have basement doors that suck shut once the furnace/AC turns on. The basement is depressurized by the leaky return ducts and relatively tight supply ducts. These pressure problems will markedly increase infiltration, which is pretty much the opposite of what you want during a period of crap outdoor air quality. To check for this problem:

1. Turn the furnace fan to ‘on’.
2. Facing the closed door at the top of the basement stairs, place the back of your hand at the crack base of the door.
3. If you feel air being sucked across your hand, the basement is being depressurized by the operation of the fan.
4. Now check every other door in your house for this. Take note of direction of airflow and relative quantity.

Fixing pressure problems is generally easy, especially in basements. Either leave the doors open or create a transfer path (usually dual grilles across the wall). Bedrooms are more difficult due to privacy considerations, but pressure problems are less common there.

3. Once you lose power, filter incoming air. Try to ride out the power outage with minimal outdoor infiltration. I think you know this already, but opening your windows when outdoor air quality is worse than indoor air quality is a mistake. This will make your indoor filtration system have to work much harder because you’re increasing the indoor contaminants. However, those same MERV 14 filters could probably be modified to seal cracks in windows and filter incoming air. So you might consider sealing the opening in windows with filter fabric. Also, there’s some possibility that you could either manually pump air through the filter at the window or install a fan that sucks air into the room through the filter. I believe Panasonic still makes some of the lowest power fans available. Their cheapest 80 cfm fan uses 24 watts. To oversimplify, a standard ventilation requirement is for ~15 cfm per person (ASHRAE 62.2), so you might run this 1/3 time or so around 0.2 kwh/day, which is super low. Also, the positive pressurization of the room should buffer against other sources of infiltration which is sort of a bonus.

What type of gas heater is in the upstairs room? Is it vented or unvented?

 

Jesse, some of what you’re saying about pressure is going over my head — I don’t have enough context or technical knowledge — but for me running the heater won’t work anyway. I have a super primitive heater. It doesn’t have a fan setting that doesn’t turn on the heat. The upstairs heater is for only one room. I actually don’t know how it’s set up. I don’t think it has a fan function, but I’d have to check — I don’t live in that room so I’d have to intrude on my housemate.

However, I had an idea for a very primitive, emergency solution. Tell me if you think this is too ridiculous. I found this cheap, passive air filter that goes on double hung windows. https://www.homedepot.com/p/Activated-Carbon-Passive-Window-Air-Purifier-AC-736/206173822. (That would fit my windows. I’m not sure about what kinds of windows my teacher has or what’s available for that, but I would guess some filter could be adapted to whatever window type she has.)

I also have this little hand-held travel fan that I love. https://www.amazon.com/OPOLAR-Handheld-Operated-Personal-Rechargeable/dp/B01MT8XBKN/ref=sr_1_10?dchild=1&keywords=opolar+handheld+fan&qid=1593715407&sr=8-10. It’s quite powerful for how little it is and very versatile as far as positioning. I’ve taken it on trips abroad where it was not only my fan on the plane but also my primary fan at my destination, keeping me cool while I slept. These little fans are chargeable through a USB, so can be charged via a power bank, or whatever. They don’t draw much power when they’re plugged into the AC. I just measured mine. It draws 4.5 watts at its highest setting and 3.4 watts at the medium setting.

So, my hair-brained scheme for bad air and no power is this. Create a very primitive clean-ish air room by doing the following. Buy a passive filter for one or both windows in my bedroom. When the air starts getting bad put in the filter. It will block some airflow, but at least let some air in. Block off possible air flow from other parts of the house by putting down something at the door crack. Purchase a couple of extra little fans and run two or three of them at a time to create some air circulation and cool the room down. The fans could probably be charged just from a portable solar panel via a power bank, although I now have the Bluetti solar generator (no solar panels for it yet though). Maybe I might also get some filters for other windows in the house so at least I can leave a window or two open there too. The other parts of the house leak air like crazy though (e.g. remember I mentioned the window that doesn’t fully close) so it might not even make sense to filter the air coming in.

Could this work in a pinch?

 

Overall very similar to #3 in what I posted above. However, I don’t know much about carbon filters and aren’t aware of a rating system for them. This could be just my ignorance, but my preference is to use things with verifiable rating systems. Thus the reco for MERV 14 filter. You could probably safely go as low as MERV 12 per article I linked earlier. Here’s a MERV 13 filter: https://www.amazon.com/Filtrete-AD23-2PK-6E-Air-Filter-Pack/dp/B07CTPSCVH/ref=sr_1_4?dchild=1&keywords=1%22+merv+14+filter&qid=1594652988&sr=8-4

To drive air through the filter you’re going to need to directly attach a fan to drive air through the filter. A low powered hand fan probably won’t be sufficient. For a manual fan consider a Kearney air pump. For a powered fan you could use a bathroom fan, but you’d have to connect it directly to a box with the filter:

https://en.wikipedia.org/wiki/Kearny_air_pump

https://www.supplyhouse.com/Panasonic-FV-0510VS1-WhisperValue-DC-50-80-100-CFM-Ventilation-Fan

To be clear, the net effect of running circulating fans is to elevate the room temperature. Electrical energy becomes heat. Fans make humans feel cooler via evaporation. But fans don’t *cool*.

Re – furnace – this is more likely a function of thermostat rather than furnace, unless it’s something totally crazy. The cheapest digital thermostats typically have an independent control for the fan, so it might be worth replacing the thermostat. If you can post the nameplate data of the furnace it should be easy to verify that this will work. In most furnaces this is just inside the upper cabinet door. Remember, it’s generally more effective to filter this way than it is to run air purifiers, so it might be worthwhile to spend a bit of time on this.

Room heater – the reason I’m harping on about this has nothing to do with opportunities for using it to filter air. I do a fair bit of carbon monoxide diagnostics, so hearing about combustion-based room heaters give me heart palpitations. Does this device have a chimney that exhausts to the outside? Do you have carbon monoxide detectors?

 

Unfortunately, my mechanical and DIY skills are such that you lost me with that last response. Let me go back to my simplistic proposal for a second and clarify. I was thinking that I could just put a filter in the window and air would come through the filter with no electrical power necessary. The carbon filters say that they do let air through, though not as much as an open window without a filter. I guess you’re saying the MERV filters won’t do that unless there’s a fan? I was trying to eliminate the use of electricity for letting in filtered air. IN ADDITION to that, I’m proposing the use of mini fans to stay cool — not to drive air through the filters. Again, they take a small amount of electricity which could be recharged with a portable solar panel if needed. Would this work as a survival type situation for a few days? (Remember, I’m also trying to think about how to set something up for my teacher, who doesn’t have a solar generator and may not have space for much in the way of full size solar panels.)

Now to your proposals. As I understand you’re suggesting that I either filter air through my heater or somehow by putting a fan in the window to suck in air through the filter, right? I don’t really understand how to rig these things up. The kearney pump seems like something that I would have to build, which I have no idea how to do. And then would I just pump it continuously? The other ones would require electricity, which brings us back to the original problem. What am I missing here?  (Also,l I have no idea where my heater plugs into the electrical grid, so I wouldn’t know hot to plug it into my generator if the electricity goes out.)

I already have an air filter. I guess you’re saying it’s not as efficient as the other solutions, but it is plug and play if the electricity holds out. It does still leave the question of how to bring air in from the outside, although as I’ve been saying in my house air seeps in from the outside anyway, but it doesn’t feel like it if the windows are closed, especially if the weather is hot.

 

We basically agree on putting the filter in your window, just maybe not on the type of filter you should use. I would guess the MERV 13 filters might be less restrictive and better at filtering, as they are specifically designed to do both of these. But I have no specific experience with the filter you’ve linked.

Circulating fans make people feel cooler. Whether this is effective probably depends a lot on ambient conditions and the individual in question. Definitely better than nothing.

Cresson Kearny was one of the GOAT preppers. His main idea around nuclear war preparation was to have inexperienced laypeople rapidly construct fallout shelters in 2-3 days in preparation for a Soviet attack on the US. Through Oak Ridge labs he tested this repeatedly on various groups of people, tweaking the design based on feedback. His book, Nuclear War Survival Skills can be found here: http://www.madisoncountyema.com/nwss.pdf.  The air pump can be found on page 193, and is a great intro to DIY skills. You could operate the pump through the filter intermittently through the day to provide better airflow, and potentially in the evening as the outdoor temperature drops to provide cooling.

Filtering through furnace is more effective than air purifiers at improving indoor air quality. This would be done when outdoor air quality is poor and you still have power to the furnace. This could be done in addition to air purifiers.

 

I was born in the Soviet Union and spent my first 10.5 years there. It’s always interesting to see what y’all over here were thinking about us :-).

Thanks for the KAP pump ref. (That link doesn’t work, by the way, but I found another one that does here: http://oism.org/nwss/nwss.pdf.) I’ll have to take a look at it and see if I can make sense of the instructions. So, then the next series of questions:

How would I fit a MERV filter to a window? The nice thing about the carbon filters is that they’re already made for windows. But the MERV filters look like they come in a frame, so you can’t just cut them down to size, and if you did how would you keep them in the window? Would I basically have to build my own frame for the filters?

Do the MERV filters let in some air without the suction of the pump?

Also, I don’t quite understand yet how the KAP pump pumps air or how often it has to be operated, but, would the idea be that I would put the KAP pump up to the window covered with the MERV filter and swing the pump back and forth, which would somehow suck the air through the filter more efficiently then letting the air passively enter? How much would this have to be done to provide adequate air?

 

It wasn’t personal 🙂

Adding filter to the window would be another great DIY project! You’ll need a filter that’s smaller than the window opening. Use cardboard or rigid foam to fill in the gaps between the filter and the window jamb. Masking tape won’t damage the paint, but also won’t have a very strong bond. Gorilla tape is tremendously effective, but will likely destroy the paint and leave a sticky residue when you remove it.

MERV is a rating that correlates to particulate size. The higher the number the smaller the particulate that can pass through it. However, as the filters become more restrictive to particulate they also become restrictive to airflow. In an earlier post I linked an article that suggested MERV 13 filters are effective at improving indoor air quality during fires. So it’s likely that this would also be effective at filtering incoming air. How much air they let through passively will vary a lot based on specific site factors – mainly wind and stack effect. Connecting fans will obviously increase the rate of airflow through the filter quite a bit.

https://en.wikipedia.org/wiki/Minimum_efficiency_reporting_value

Off the top of my head I don’t recall, but Kearny reported very high numbers for airflow. If accurate, you’d likely run the KAP infrequently to increase the rate of ventilation. Probably just before you go to sleep, and then intermittently throughout the day if the room feels stuffy.

Remember, the basis for doing all this is sort of slim. This is to provide ventilation for power outages during fire when you absolutely need to exchange air with the outside. The main defense against poor outdoor air quality is to reduce air leakage. Because of the need for outdoor air in spite of poor outdoor air quality, filtration becomes mandatory.

 

Are there effective ways of finding out how much air leaks and where? You mentioned something about a blower test? I don’t know what that is.

 

Yes. A blower door is often used to quantify infiltration rates. By depressurizing houses to the same level (-50 Pascals), the blower door can be used to make comparisons between houses and across the same house over time. I have a couple of blower doors, and one of my crews runs them daily.

https://www.energy.gov/energysaver/blower-door-tests

However, the reality is that rates and locations are fairly predictable, although probably counterintuitive to laypeople (ex. it’s never windows). If you’re trying to reduce leakage, start with process for evaluating HVAC fan-driven problems I outlined above. Then follow this guide for attic and basement rim joist sealing.

https://www.buildingscience.com/documents/guides-and-manuals/gm-attic-air-sealing-guide/view

 

Jesse, do you think it’s true, as somebody said in another thread, that the Kerny pump isn’t suitable for operation by a woman with “average” strength — which I guess means a woman in our society who doesn’t do a lot of physical work or work out? I don’t really know what’s meant by average. If so, it’s not a very useful tool — if it doesn’t serve a slight majority of humans!

 

The reality is that any manual fan is going to require exertion. However, Kearny’s original application would have required much longer cycles, and even then I believe was probably used intermittently. If it’s excessive you could probably slow down or take longer breaks. There’s always the pre-filter and powered fan option too. 

 

Sorry, what’s the pre-filter and powered fan option?

 

Attach a filter to an electric window fan somehow and point the fan into the room. Connect to your back-up power source during an outage. I linked a low energy bath fan somewhere on this thread, but that’s probably going to require moderate electrical and carpentry skills. So maybe a window fan on low with a filter taped to it? 

 

Jesse, do you think this would work for a situation if the air is bad but the electricity hasn’t gone out? I bought a MERV 14 filter that I plant to put in my (double hung) window. It’s not wide enough for the whole window so I plan to fill the rest with cardboard — have to figure out how to make that fit with no gaps. Maybe duct tape. Then I have a double window fan that I can put right up against the filter. Probaby only one of the fans will actually be contacting the filter. Would this pump air into the house if I have to otherwise keep windows closed?

And, followup question. Does it make sense to have another filter and fan setup in another window somewhere in the house, but this one pumping air OUT? (For better air circulation?)

 

Would you rather solve the problem by having enough energy stored (such as with batteries and an inverter) that you can plug any device into the way you would a wall outlet, or would you rather change your devices (like the fan) so that it can run on more common emergency power options (without the whole inverter setup)?

 

Either scenario would be okay with me. When you say more common emergency power options, what do you mean?

 

I mean more common / easier to get and use things like a portable solar panel. That seems easier to me than trying to store enough energy to then run through an inverter and be able to power a normal 110v wall-plug device.

 

It’s either going to run on DC power via battery/solar, or invert from DC to the AC power that’s in most buildings.  Jonnie already has a battery w inverter built-in, so I’d stick with AC powered devices, especially for domains where there’s a lot of focus on energy efficiency. It’s possible that a DC powered back-up fridge might be a good choice, as these have a broad market for boats and RVs. But things like fans and air cleaners that aren’t as common to the DC power market are likely going to be better off using inverted AC power.

 

I just also want to add that the issue of how to create breathable air when there’s no electricity (or gas) isn’t an edge case for people living in wildfire zones. In the Paradise fire, in 2018, some people couldn’t evacuate in time. Their homes and they survived but they were trapped with no services, no access to the outside world and dangerously HORRIBLE air quality for about two weeks. (I actually use the Paradise fire to proselytize preparedness to my circle of friends and acquaintances because it illustrates exactly the need for the two scenarios basic prepping strives to be ready for — bugging out at a moment’s notice, possibly on foot and sheltering in place for two weeks. Both of these scenarios played out in that fire.)

My point is that those folks had to survive in that toxic soup for two weeks. I assume most of them didn’t have generators. I’m not sure how they did it but figuring out how to breathe seems like a pretty basic prep.

 

This is a long thread and I read or skimmed through most of it so forgive me if this is repetitive. 

Hi, Oregonian here! We just did this. If your house isn’t well sealed, then use towels or bedding to cover the obvious cracks. Close all windows. Then run your filter on “fan only” mode, continuous. You can also run in A/C mode if it’s hot outside, but make sure the fan is on continuous. 

Then make one room more livable. Pick a room that is fairly small and close the door. Then get a box fan and Merv 13 or better furnace filter (just added a bunch of these to our prep!). Attach the furnace filter to the back of the fan with the arrows pointing toward the fan. Put the fan in the center of the room and turn it on low. It will clean the air in the room. (Supervise it because it can overheat easily). 

So, if you close up your bedroom at night, you need a generator that can run your CPAP and a box fan at the same time. And if you have “air hunger” at night, then instead of opening a window, try turning the fan so it blows air on your face. Or get a small battery powered fan for that. (I’m an RN and that really helps all my COPD patients.)

 

Meant to say run your FURNACE on fan only. 

 

Hi Jonnie, a bit off topic, but one thing to ask your doctor about is an “oral appliance” that helps with sleep apnea. It’s a mouth-piece that’s small and requires no electricity.  I have one and it works great and is fantastic for traveling and such.  It might be a good backup for you in case of electrical outage.  

 

Hey Jonnie, I found a cool website called purple air that shows current air quality.

 

Just saw your post Robert about Purple Air, and that’s actually what one of our latest blog posts is about. Review: I installed a PurpleAir personal Air Quality Index meter that helps the public with open data

 

Hi Jonnie Pekelny.

The Prepared released a blog post written by another forum user about an air quality index meter that I thought was fitting for this topic and something you would be interested in.